Epigenetic modifications, including chromatin structure modification, DNA and histones covalent and non-covalent modification, nucleosome and small non-coding RNAs remodeling, are fundamental in controlling the normal development and maintenance of gene expression. Epigenetic alteration in general infers changes of gene expression, which is reversible and heritable, without altering the DNA sequence. The onset of diseases have been identified to be associated with abnormal epigenetic regulation. For example, aberrant. DNA methylation in the promoter regions of tumor suppressor genes plays a critical role in cancer development and progression.
DNA methylation, the addition of a methyl group to the fifth carbon position of a cytosine residue by DNA methyltransferase (DNMT), occurs in CpG dinucleotides and is a key epigenetic feature of the human genome. These dinucleotides are usually distributed within stretches of 1- to 2-kb GC-rich DNA, named CpG islands, located in the promoter and/or first exon of 60% of human genes. Promoter methylation is known to participate in reorganizing chromatin structure and also plays a role in transcriptional inactivation.
Hypermethylation of promoters of tumor suppressor genes such as ESR1 (estrogen receptor α) in colorectal and breast cancers, GSTP1 (glutathione S-transferase) in breast and prostate cancers, RARβ2 (retinoid acid receptor β2) in colorectal, breast and prostate cancers, DAPK1 (death-associated protein kinase 1) in breast and lung cancers, have been linked to cancer development and progression in human. Prostate cancer (PCa) is the most commonly diagnosed male cancer (⅙ men in their lifetime) and the second leading cancer related death in men in the USA. Prostate cancer has a very long latency period involving a cascade of epigenetic and genetic changes. Epidemiological, experimental, preclinical, and clinical studies have shown that long-term oxidative stress and chronic inflammatory status would drive the development and progression of PCa.
When cells are exposed to excessive oxidative stress, DNA goes through oxidative damage. When coupled with chronic inflammation and with formation of DNA adducts, this leads to enhanced genomic instability, neoplastic transformation and ultimately drives cancer formation and tumorigenesis. To counteract oxidative stress, induction of various cellular protective enzymes including phase II drug metabolizing enzymes (DME), phase III transporters and antioxidant enzymes occur. Carcinogens are typically metabolized via oxidation and reduction by phase I DME. The resulting products subsequently undergo phase II conjugations catalyzed by phase II DME enzymes such as glutathione S-transferases (GST) and UDP-glucuronosyltransferases (UGT), resulting in the formation of metabolic products which are more water soluble and can be easily excreted in the urine and the bile.
The induction of phase II enzymes can be largely attributed to the transcriptional control of the antioxidant response element by the nuclear factor (erythroid-derived 2)-like 2 (NFE2L2 or Nrf2). Nrf2 is known as a key regulator of the antioxidant response element (ARE)-mediated gene expression and therefore a potential target for cancer chemopreventive compounds. Nrf2 is inhibited in the cytoplasm by the anchor protein Kelch-like ECH-associated protein-1 (Keap1) and in the presence of oxidative stress or chemical inducers. Nrf2 is released from Keap1 inhibition, translocates to the nucleus, dimerizes with small dais and binds to ARE consensus sequence. Regulation of Nrf2 by cancer chemopreventive agents would lead to the induction of gene expression of phase H and anti-oxidative stress enzymes such as heme oxygenase 1 (HO-1). HO-1 catalyzes the degradation of heme to carbon monoxide, iron and biliverdin. HO-1 is critically essential in cellular defensive mechanisms and is implicated with various pathophysiological conditions such as inflammation, atherosclerosis, neurodegenerative diseases and cancers.
Phytochemicals, such as indoles and isothiocyanates (ITCs) possess potent chemopreventive effects. Previous studies show that the indoles achieve the chemopreventive effects via multi-targets. Interest on the dietary indoles has moved beyond preclinical testing and most recently, oral DIM of 2 mg/kg/day has been found to be well tolerated with no significant toxicity. Similarly, oral I3C is also well tolerated. Increasing evidence from in vitro, in vivo and clinical studies have supported the rational use of multi-targeted therapies for cancer treatment and prevention, as well as administration of combinations of conventional chemotherapeutic agents with natural phytochemicals. Indoles are capable of inducing antioxidant activity, regulate cellular proliferative genes, induce cell cycle arrest/apoptosis, regulate hormone metabolism and stimulate the immune system. ITCs also elicit their chemopreventive effects via various mechanisms such as regulating DME phase I cytochrome P450s and phase II, regulating Nrf2-Keap1 signaling and anti-inflammatory NFkB pathways, and inducing cell cycle arrest/apoptosis.
Clinically, advanced and metastasized cancers in humans are very tough to treat, resistant to radiation and chemotherapy because of too numerous epigenetics, genetics and loss of heterozygocity (LOH), among others. Hence it would be logical and clinically feasible if one could utilize relatively non-toxic dietary phytochemicals and or medicinal drugs such as NSAIDs, to prevent, block or delay the progression of benign tumors from becoming advanced/metastasized cancers. Increasing evidence suggests, for example, that during prostatic carcinogenesis, epigenetic changes arise earlier than genetic defects, linking the appearance of epigenetic alterations in some way to disease etiology.
Many relatively non-toxic dietary phytochemicals such as polyphenols from green tea and isothiocyanates from plant food have been shown to inhibit cancer development via epigenetic mechanisms both in vivo and in vitro. Recently, curcumin. a potent anti-cancer agent in many cancer models including PCa, has been found to suppress the expression of DNA methyltransferase (DNMT) and histone deacetylase (HDAC) in the human prostate LNCaP cells and reverses the DNA CpG hypermethylation of the promoter region of Nrf2 in TRAMP C1 cells and Neurog1 in LNCaP cells.
Cruciferous vegetables contain abundant phytochemicals with superior potential in cancer chemopreventive activities. Cruciferous vegetables include broccoli, Brussels sprouts, cabbage and cauliflower and are rich in glucosinolates that can endogenously be converted into compounds including indoles indole-3-carbinol (I3C) and 3,3′-diindolylmethane (DIM)) and ITCs phenethyl isothiocyanate (PEITC) and sulforaphane (SFN)) upon ingestion.
Applicants have recognized, however, that there is a need in the art to understand the mechanism by which indoles (I3C and DIM) a id ITCs (SFN and PEITC) provide chemopreventative activity.
Applicants have recognized that there is a need in the art to understand the mechanism by which indoles and ITCs provide chemopreventative activity and inhibit tumorigenesis, and whether an epigenetic mechanism might be involved. Applicants have recognized that understanding such mechanisms may aid in defining methods of treating or preventing cancer by administering such compounds. The present invention addresses these needs, among others.